1. Field of the Invention
The present invention relates generally to the joining of flat woven fabrics to render them endless. More particularly, the invention relates to joining papermakers wet press felt base fabrics to render them endless. Most particularly, the present invention relates to joining flat woven papermakers wet press felt base fabrics having crimped machine direction yarns.
2. Description of the Prior Art
It is known to join a flat woven fabric in order to render it endless. In the earliest fabrics, the woven yarns were generally natural fibers, such as cotton, wool and combinations thereof. Due to the nature of the natural fiber, the joined area receives some of its mechanical strength from the natural resistance of the fibers pulling past each other and additional strength from the fiber migration which took place during fulling of the felt. The join area in these fabrics are generally quite large and may extend over several feet.
With the advent of synthetic monofiliments which have more regular and smoother surface characteristics, thee was a tremendous reduction in the mechanical strength attributable to fiber movement resistance. Similarly, the practice of fulling was no longer part of the finishing operations for the press felt. Accordingly, the mechanical strength generally associated with fiber entanglement as a result of fulling was no longer a major factor in seam strength.
As a result of the above, the art developed a number of joining techniques to produce the required mechanical strength. One of the principle drawbacks of the prior art join was the large joining area which was still necessary to accomplish mechanical strength. It is believed that the need for a large join area is directly related to the weave construction of the prior art fabrics wherein the crimp was generally in the cross machine direction yarns and a number of cross machine direction yarns had to be involved in order to accomplish the joining structure. Although the synthetic monofiliments generally maintain their crimp memory, lack of crimp in the machine or running direction of the fabric necessitated large joining areas. The length of the fabric seam is generally determined by the same strength which is necessary to maintain the fabric under the running load or tension associated with fabric operation. It is not uncommon to have a fabric running load of 20 pli (pounds per lineal inch). Under this load, the typical press felt fabric would have a minimum seam length of about ten (10) inches.
In view of the above, efforts were undertaken to reduce the size of the join area and to improve the uniformity in the join area. Along with improved uniformity and reduced size, the art desired a join which had improved resiliency to compression in the nip area of the papermaking machine. It was found that the use of machine direction crimp in the flat woven fabric produced a crimp pattern which accurately reflected the fabric weave. Once the woven fabric was heat set, the machine direction yarns have a fixed memory of the crimp pattern which means that the join area may be rewoven in the precise pattern of the original flat woven fabric. As a result, the endless fabric will have substantially the identical pattern, caliper and air permeability through its length.
The warp yarns are crimped as a result of the inner weaving with cross machine direction yarns and heat setting. The yarn memory for this crimp permits reweaving of the fabric to join the fabric ends to achieve mechanical strength based on the initial crimp patterns established during the weaving. In this manner, the resultant fabric join area establishes essentially the same weave pattern as if the pattern had been woven endless in the first instance. However, fabrics according to the present invention can include much higher machine direction yarn counts then would be available with a similar fabric which had been woven endless.